The instant invention is in the field of chemical compounds comprising polyoxyalkylene sub-structures such as polyethylene glycol sub-structures. The instant invention also relates to methods for producing chemical compounds comprising polyoxyalkylene sub-structures.
Biologically active compounds comprising polyoxyalkylene sub-structures can provide enhanced biocompatibility for the compound, See, for example, U.S. Pat. No. 5,366,735 and U.S. Pat. No. 6,280,745. A review of this subject by Zalipsky, in Bioconjugate Chem., 1995, 6, p 150-165, identified polyethylene glycol as one of the best biocompatible polymers to conjugate with a biologically active compound, such as a drug, a protein, or an enzyme, to produce a conjugate having improved properties such as compatible solubility characteristics, reduced toxicity and reduced immunogenicity.
Polyethylene glycol (PEG) is a linear or branched polyoxyalkylene terminated at the ends thereof with hydroxyl groups and generally represented by the formula: HO—(CH2CH2O)n—CH2CH2—OH. As discussed by Henmanson in Chapter 15 of Bioconjugate Techniques (1966), monomethoxy polyethylene glycol (mPEG) generally represented by the formula: CH3O—(CH2CH2O)—CH2CH2—OH, is usually used to prepare a polyethylene glycol conjugate with a biologically active compound typically by way of a coupling reaction between an amine group of the biologically active compound and an amine receptive derivative, such as trichloro-s-triazine activated mPEG, formed via the remaining terminal hydroxyl group of the monomethoxy polyethylene glycol. An acrylate terminated PEG is offered commercially by Shearwater Corporation (Huntsville, Ala.) for vinyl polymerization or co-polymerization to produce graft polymers or cross-linked materials with excellent properties for biomaterial applications.
More recently, so called “second generation” PEGylation chemistry has been developed to, for example, minimize problems of diol impurity contamination of mPEG, to increase the molecular weight of the polyoxyalkylene sub-structure and to increase stability of the conjugate, see Roberts et al., Advanced Drug Delivery Reviews 54 (2002) p 459-476.
Dendrimers are hyperbranched, uniformly distributed structures, having, at least ideally, definite molecular weight, shape and nanometer size characteristics. Dendrimers were discovered by inventors at the Dow Chemical Company, see Polym. J. 17 (1985) p 117-132. Dendrimers have been widely studied as a drug delivery means, see for example Knusli et al., J. Haematology, 82, 654 (1992). Dendrimers carrying the anti cancer drug 5-fluorouracil have been PEGylated to reduce hemolytic toxicity, drug leakage and macrophageal uptake while improving stability and efficacy, see Bhadra et al., International Journal of Pharmaceutics 257 (2003) p 111-124.
PAMAM dendrimers are the most common type of dendrimer and are commercially available from Aldrich (Milwaukee, Wis.) in the form of various “generations”. PAMAM dendrimers are made by a successive Michael addition synthesis scheme involving the reaction of an acrylate group with an amine group. The so called “Generation 0” PAMAM dendrimer has the following formula:

The above Generation 0 PAMAM dendrimer has a molecular weight of about 517 grams per mole. A Generation 1 PAMAM dendrimer has a molecular weight of about 1,430 grams per mole and has eight terminal primary amine groups. A Generation 2 PAMAM dendrimer has a molecular weight of about 3,256 grams per mole and has sixteen terminal primary amine groups. A Generation 10 PAMAM dendrimer has a theoretical molecular weight of almost 935 kilograms per mole and in theory has 4096 primary amine groups on the surface of the dendrimer.
Despite the significant advances that have been made in the field of methods for the PEGylation of biologically active compounds, and more generally in the field of methods for the conjugation of polyoxyalkylene sub-structures with biologically active compounds, the existing methods generally require multiple reactions and extensive purification of the product. It would be an advance in this art if a process was discovered that required only one reaction step and produced no by-products.